The present invention relates essentially to the ceramic substrate, ceramic heater, electrostatic chuck and substrate for the wafer prober for semiconductor manufacture and/or inspection and more particularly to a ceramic substrate for semiconductor manufacture and/or inspection which is conducive to the prevention of electrical errors, decrease in electrostatic chucking power, and the suppression of generation of lattice defects of the silicon wafer.
Semiconductor devices are manufactured through a process which comprises coating a photosensitive resin as an etching resist on a semiconductor wafer and etching the uncoated area.
While the photosensitive resin is applied in the form of a liquid to the surface of a semiconductor wafer by means of a spin coater or the like, it must be dried after coating to dissipate the solvent etc. and the thus-coated semiconductor wafer is set on a heater and heated.
The conventional metallic heater heretofore used for this purpose comprises a resistance heating element disposed on the reverse side of an aluminum plate.
However, such a metallic heater has the following disadvantages.
First, because it comprises a metallic material, the heater plate must be as thick as about 15 mm. This is because a thin metal plate undergoes thermal expansion on the heating mode to develop a curl and strains to damage or tip the semiconductor wafer placed on the metal plate. However, increasing the thickness of the heater plate leads to increases in heater weight and bulk.
Moreover, while the heater temperature is controlled by varying the voltage and current applied to the resistance heating element, the great thickness of the metal plate causes the problem that the temperature of the heater plate cannot timely follow changes in voltage and current values, thus making temperature control difficult.
Therefore, Japanese Kokai Publication Hei-9-306642 and Japanese Kokai Publication Hei-4-324276, for instance, proposed ceramic heaters each comprising a substrate board comprising AlN, which is a non-oxide ceramic material of high thermal conductivity and high strength, and a resistance heating element formed internally of said substrate board.
Furthermore, JP 2798570 discloses an electrostatic chuck comprising an AlN substrate, a resistance heating element formed therein, and, for the purpose of attracting and setting in position a semiconductor wafer on a heater, static electrodes as embedded in said AlN substrate.
However, when such a heater or an electrostatic chuck having a resistance heating element formed in an AlN substrate is employed, as compared with a heater based on an aluminum plate, there are encountered incomprehensible phenomenon that an accurate temperature control becomes difficult with passage of the time.
Initially, malfunction of the apparatus itself was supposed for the reason of the phenomenon, however, it has proved that the accurate temperature control cannot be conducted even though the heater and the like are brought into the direct contact with the ceramic.
The inventors scrutinized such a problem inherent in the prior art and found surprisingly that the cause of the trouble lies in the xcex1-rays radiated from the ceramic substrate and that by controlling the level of those xcex1-rays below a given value, the accurate temperature control can be possible even after passage of the time. Based on these findings, inventors have completed the present invention.
That is, the present invention is a ceramic substrate for apparatus for use in semiconductor manufacture and/or inspection, which is used under the temperature adjustment condition such as heating or cooling,
wherein the level of xcex1-rays radiated from the ceramic substrate exceeds 0.25 c/cm2xc2x7hr and is not higher than 50 c/cm2xc2x7hr.
Also, the ceramic heater using the ceramic substrate of the present invention is a ceramic heater, for heating a semiconductor, comprising a ceramic substrate and a heating element disposed on the surface or internally thereof,
wherein the level of xcex1-rays radiated from the ceramic substrate exceeds 0.25 c/cm2xc2x7hr and is not higher than 50 c/cm2xc2x7hr.
In addition, the electrostatic chuck of the present invention is an electrostatic chuck comprising a ceramic substrate and electrodes (electrostatic electrodes) embedded therein,
wherein the level of xcex1-rays radiated from the ceramic substrate exceeds 0.25 c/cm2xc2x7hr and is not higher than 50 c/cm2xc2x7hr.
Further, the substrate for the wafer prober of the present invention is a substrate for a wafer prober comprising a ceramic substrate and a conductor layer formed on the surface thereof,
wherein the level of xcex1-rays radiated from the surface (conductive layer formed surface) of the ceramic substrate exceeds 0.25 c/cm2xc2x7hr and is not higher than 50 c/cm2xc2x7hr.